In our foundry, the production of urban rail gearbox casting parts faced significant challenges due to the traditional floor-type manual molding process. With an annual output exceeding 10,000 sets of these critical casting parts, the operation relied on two production shifts, each with eight workers, leading to inefficiencies such as frequent handling, prolonged waiting times, and high physical labor intensity. The production rhythm was largely driven by subjective decisions of frontline workers, resulting in low efficiency, inadequate execution of production plans, and frequent overtime to meet batch order deliveries. This situation underscored the urgent need to enhance the “digital-intelligent” construction level of the workshop by establishing an intelligent, rhythmic molding production line to boost productivity, reduce labor intensity, and ensure timely delivery of casting parts. This initiative became a primary goal in our company’s push towards intelligent transformation and digital upgrading.
Guided by lean production theory, our approach focused on eliminating waste, including rework, erroneous production,无效 and excessive processes, non-value-added activities, transportation, and waiting. The core work comprised three parts: production line design, production process optimization, and production line operation. Among these, the design phase served as the foundation, requiring the determination of line parameters and operation modes based on product工艺 requirements to maximize improvement effects.
Design of the Molding Production Line
We aimed to connect molding production equipment via specific conveying devices to build a production line that operates on a station-based, rhythmic production model. This shift from a scattered floor layout to a streamlined flow was crucial for handling casting parts efficiently.
Production Rhythm Design
The production rhythm, or takt time, defines the time required to produce a single unit, reflecting the line’s capacity and efficiency. Originally, the molding process for urban rail gearbox casting parts involved floor-type production with steps like molding, pattern stripping, coating, core setting, and mold closing. Two shifts produced 36 sets daily, totaling 72 boxes.
Through analysis and time studies of the production流程 for these casting parts, we identified that the longest固化 time for a single outer mold was approximately 7 minutes, representing the bottleneck. To achieve high-efficiency rhythmic production and maximize capacity, we set the theoretical optimal takt time at 7 minutes per box, meaning each station must complete its tasks within this interval.
However, with单一 product production,模具 waiting times were long due to the need for脱模 and tooling preparation. If based solely on the 7-minute takt, demand couldn’t be met. Thus, we simulated production with two types of gearbox casting parts (each with upper and lower boxes, totaling 8 pattern plates). The daily output formula is:
$$
Pt = \frac{6 \times 60 \text{ min}}{N} = 7 \text{ min/box}
$$
where \( Pt \) is the production takt in minutes per box, and \( N \) is the daily output in boxes. Calculating this, and considering actual working hours of 6 hours per shift, the theoretical single-shift capacity reached 26 sets or 52 boxes. This highlighted the potential for scaling up the production of casting parts.
Station Design
A station is where a product pauses relatively on the line for workers to complete assigned tasks within one takt. As the最小 production unit, a line consists of multiple connected stations.
By charting the process mountain plot for gearbox casting parts molding, we observed imbalances in作业 times between stations. The existing station tasks included unnecessary handling, so we redesigned the process with同期化 principles. We merged pattern stripping and coating into one station, split molding into辅助 and main molding steps, and eliminated three吊运 operations to reduce waste. After optimization, we established six production stations: Molding辅助, Molding, Pattern Stripping & Coating, Core Setting, Mold Closing, and Fastening & Transport. This reorganization streamlined the flow for casting parts.
| Original Station | Time (hours) | Optimized Station | Time (hours) |
|---|---|---|---|
| Molding & Sand Filling | 2 | Molding辅助 | 1.5 |
| Pattern Stripping | 1 | Molding | 1.5 |
| Cleaning | 0.5 | Pattern Stripping & Coating | 1 |
| Coating | 4 | Core Setting | 1 |
| Core Setting | 2 | Mold Closing | 1 |
| Mold Closing | 1.5 | Fastening & Transport | 1 |
| Transport | 0.5 | – | – |
Automation Design
High-intensity manual labor in traditional sand casting hindered sustainability, as young workers were reluctant to engage in such tasks, leading to recruitment difficulties. Originally, 16 workers were needed across two shifts for 36 sets daily, with coating taking 4 hours and causing delays. Tasks like mold flipping required three people to handle 420 kg sand molds, posing efficiency, safety, and ergonomic issues.
To reduce dependence on manual labor and minimize waste, we focused on:
- Designing line height and工装 according to ergonomics to eliminate bending or kneeling.
- Implementing synchronous flipping mechanisms at two关键 stations: one covering pattern stripping and coating, and another for mold closing, thus removing heavy physical work.
- Enabling automatic transport of molds and sand molds to designated stations based on production logic.
- Incorporating line循环 functions, such as angle adjustment during pattern stripping via flippers.
- Setting up专用 core-setting吊具 and using同步 flipping for mold closing, reducing reliance on cranes.
This automation led to a U-shaped line layout, 35 meters long, enabling single-piece flow and rhythmic production for casting parts. The line uses roller conveyors, control programs, flipping devices, coating machines, and dust/VOC treatment systems to enhance efficiency.
Optimization of Production Processes
Production process optimization encompasses material management, personnel allocation, equipment, standard作业, and digital-intelligent construction. Aimed at拉动产能 and lean cost management, it focuses on流程 improvement and reducing non-value-added activities to cut waste and costs for casting parts production.
Material Management
We established a material distribution mechanism to ensure first-in-first-out flow and orderly投入, eliminating material waste. By analyzing material types and制定配送流程, we implemented quota-based distribution. This involved setting up a distribution team, tools, and a material information database covering all production materials.
For instance, with iron chills—widely used in molding casting parts—we created回收 points at shakeout stations for centralized collection. Distribution personnel then sort and deliver them in sets according to production plans, as shown in the process below:
| Step | Action | Outcome |
|---|---|---|
| 1 | Set up回收 points at shakeout | 定点回收 of chills |
| 2 | Collection and sorting by distributors | 分类处理 |
| 3 | Quantitative delivery based on plan | 成套配送 to production |
Station Optimization and Personnel Allocation
Labor costs are a significant portion of total expenses in resin sand casting. Optimizing personnel allocation is essential to maximize human resource utilization. Originally, floor-type production relied heavily on manual effort: molding required three workers (1.5 for sand filling, 1.5 for stripping), and coating needed two. After optimization, only three workers handle tasks previously done by five, with molding reduced to 1.5 workers and coating to one, eliminating two吊运 operations.
Following同期化 principles, we assigned one worker per station across the six stations,定岗定人, reducing shift headcount from 8 to 6. This cut labor costs while increasing output for casting parts. The daily efficiency improved from 2.25 sets per hour to 4.33 sets per hour.
| Production Mode | Workers per Shift | Daily Output (Sets) | Efficiency (Sets/Hour) |
|---|---|---|---|
| Floor-type | 8 | 36 | 2.25 |
| Production Line | 6 | 52 | 4.33 |
Equipment and Facilities
Based on takt time and station design, key equipment includes roller conveyor devices, control programs, flipping mechanisms, coating machines, dust removal, and VOC treatment systems. We specified line dimensions, power supply, environment, and dust collection to enable automatic mold循环 and controlled sand mold flow.
| Item | Quantity | Main Parameters |
|---|---|---|
| Vibrating Table | 1 | Z294, load: 5 t, table size: 2800×1350 mm, power: 2×3.7 kW |
| 机动 Roller Conveyors | 7 | JDGD100, B=1000 mm, L=2900 mm, power: 1.5 kW each |
| Transfer Cars | 2 | ZYCA & ZYCB, load: 5 t, power: 2×1.5 kW and (2×1.5+1.1) kW |
| Servo Cranes | 4 | DF+63SD1-3200+3200 frequency conversion servo |
| Dust Removal Fan | 1 | 55 kW, air volume: 35,000 m³/h, pressure: 3,500 Pa |
| VOC Treatment Tower | 1 | Diameter 2 m, two-stage spray |
The dust removal system uses斜装 filter cartridges with pulse jet cleaning, and variable frequency control ensures emission concentration below 15 mg/m³, creating a cleaner environment for producing casting parts.
Standard作业
Standard作业 is fundamental for rhythmic production, involving scientific work steps to achieve efficiency and cost savings. For our casting parts, we redesigned standard tasks based on工艺, optimizing流程, sequence, time, and quality control points. For example, adjusting固化剂 dosage and sand temperature ensured uniform curing, while coating density was optimized to 48–52 Baumé to prevent堆积 and流挂 during coating.
We compiled standard作业 documents for all six stations. Below is an excerpt for the Pattern Stripping & Coating station:
| Step | Time (s) | 作业 Steps | Key Points |
|---|---|---|---|
| 1 | 41 | Pattern Stripping | Vertical stripping; avoid斜吊 |
| 2 | 47 | Mold Cleaning | Clean碎砂 around risers and chills |
| 3 | 30 | Riser Protection & Coating | Control coating density; apply evenly |
| 4 | 30 | Transfer to Line & Ignition | Ignite only after transfer; quick ignition |
| 5 | 1 | In-process Transport | Ensure positioning at designated spot |
Digital-Intelligent Construction
Integrating information technology transformed our management模式, optimizing production workflows through digital tools. The production line features a digital智能 electronic display board that visualizes real-time production status and task completion, replacing paper records and offering error-proofing by showing作业 instructions and product codes to prevent material misplacement or duplicate casting parts.
The system enhances traceability and efficiency, aligning with our goal of intelligent manufacturing for high-quality casting parts.
Operation of the Production Line
Prior to deployment, we formed a team to collect and address issues during trial runs, resolving problems related to programs, leveling, and conveyor slippage. We also identified hazards, established maintenance benchmarks, and conducted training, with operators regularly completing equipment checklists.
The line simplifies operations by merging and eliminating steps, balancing作业 times across six stations. It is adaptable to over 100 products, including urban rail and locomotive gearbox casting parts. Mechanical and automated handling of in-process items reduces物流周转, lowers labor intensity, eliminates safety risks, and frees up approximately 2,600 m² of floor space. To further enhance station capability, we designed various工装 for organized material placement, minimizing bending and walking.
The benefits are summarized in the table below:
| Metric | Before Implementation | After Implementation | Improvement |
|---|---|---|---|
| Daily Output of Casting Parts | 36 sets | 50+ sets | ≈38% increase |
| Workers per Day | 16 | 14 | 12.5% reduction |
| Product Quality (Defect Reduction) | Baseline | 1% improvement | Due to less handling振动 |
| Safety | Frequent crane/forklift交叉 | Reduced交叉 operation | Enhanced intrinsic safety |
| Environmental Impact | Limited dust/VOC control | Effective collection & treatment | Cleaner production |
Conclusion
The implementation of an intelligent, rhythmic molding production line based on station-driven takt production has revolutionized our manufacturing of urban rail gearbox casting parts. By adopting a resin sand molding approach and leveraging mechanization to replace manual labor, we have significantly increased产能, reduced physical strain, saved labor costs, and improved quality management. This transformation aligns with the trends towards green casting and digital-intelligent manufacturing, ensuring sustainable production of high-demand casting parts. The line not only meets batch delivery requirements but also fosters a safer, more efficient workshop environment, positioning our company for future growth in the casting industry.